The present invention relates to a continuous forming method for Ti/TiN film, and more particularly to a Ti/TiN film continuous forming method for freely controlling a TiN film forming process so that a TiN film formed has such film quality as a nitride TiN film or a metallic mode TiN film in the TiN film forming process.
Following high-integration design of semiconductor devices, more minute and more multiple layer structure is being promoted for the wiring structure. As such an enhancement in minuteness and layer-multiplicity of the wiring structure is promoted, a multiple-layer wiring technique is growing more sophisticated technologically, and the technical position which the multiple-layer wiring technique occupies in the manufacturing process for semiconductor integrated circuits is more and more important.
Particularly for semiconductor devices based on the design rule subsequent to 0.5 .mu.m are increasingly used such a wiring structure that metal of high melting point such as titanium (hereinafter referred to as "Ti"), titanium nitride (hereinafter referred to as "TiN") or the like is laminated as barrier metal on the upper or lower surface of aluminum alloy formed as a wiring film, for example, Al--Si film, Al--Si--Cu film or the like, or on both the upper and lower surfaces thereof.
Here, the conventional laminated wiring structure having a high melting point metal film as barrier metal will be described with reference to FIGS. 1A to 1D. FIGS. 1A to 1D are cross-sectional views showing various wiring structures.
The wiring structure shown in FIG. 1A is a laminated wire comprising a Ti film 11 of 20 nm in thickness, and a TiN film 12 of 70 nm in thickness which is formed on the Ti film 11.
The wiring structure shown in FIG. 1B is a laminated wire comprising a Ti film 13 of 20 nm in thickness, a TiN/Ti film 14 of 20 nm/5 nm in thickness respectively, an Al--Cu film 15 of 500 nm in thickness and a Ti/TiN/Ti film 16 of 5 nm/100 nm/5 nm in thickness respectively, these films being successively formed in this order.
The wiring structure shown in FIG. 1C is a laminated wire comprising a Ti film 17 of 100 nm in thickness, a TiN/Ti film 18 of 20 nm/5 nm in thickness respectively, an Al--Cu film 19 of 500 nm in thickness and a TiN/Ti film 20 of 35 nm/5 nm in thickness respectively, these films being successively formed in this order.
The wiring structure shown in FIG. 1D is a laminated wire comprising a Ti film 21 of 200 nm in thickness, a TiN/Ti film 22 of 20 nm/5 nm in thickness respectively, an Al--Si film 23 of 900 nm in thickness, and a TiN film 24 of 35 nm in thickness, these films being successively formed in this order.
As described above, wires having the laminated wiring structure containing five to seven layers have been used in semiconductor devices mass-produced in the 0.35 .mu.m design rule generation.
A so-called multi-chamber type sputtering device is used to form the laminated wiring structures shown in FIGS. 1A to 1D. Here, the construction of the multi-chamber type sputtering device will be described with reference to FIG. 2. FIG. 2 is a schematic plan view showing the construction of the multi-chamber type sputtering device.
As shown in FIG. 2, the multi-chamber type sputtering device has plural process chambers each containing a sputtering material (target) which is connected with the kind of each film formed (hereinafter referred to as "chamber"). With this multi-chamber type sputtering device, one kind of metal film is formed on a wafer by using one chamber. A wafer is sequentially fed into the plural chambers and the film formation is repeated to form a laminated film. In the multi-chamber type sputtering device, the respective wafers are sequentially processed in turn.
More specifically, the multi-chamber type sputtering device 30 includes plural chambers 32A to 32D (in the case of FIG. 2, four chambers are illustrated) in which desired targets are respectively mounted, a feeding arm 33 for feeding the wafers, a separation chamber 34 which intercommunicates with each of the chambers 32A to 32D through a gate valve (not shown), and a load lock chamber 38 which intercommunicates with the separation chamber 34 and also intercommunicates with the external through a gate valve 36.
As not shown, in each of the chambers 32A to 32D are provided a cathode electrode which will serve as a sputtering source by mounting a target of a desired sputtering material, a wafer holder for holding the wafers, a gas inlet port for reaction gas, a cryopump connected to each chamber through a discharge valve to keep the inside of the chamber under high vacuum, etc.
When a metal film is formed on a wafer by sputtering, a wafer cassette in which wafers are mounted is first automatically fed to the load lock chamber 38, and then a wafer W is fed from the wafer cassette to the separation chamber 34 by the feeding arm 33. Subsequently, the wafer W is fed into one of the chambers 32A-32D to be subjected to the sputtering process, and mounted on the wafer holder. In one of the chambers 32A-32D, a metal film is formed on the wafer on the wafer holder by the sputtering method according to a predetermined recipe.
After the film formation of the metal film is completed, the wafer is taken out from one of the chambers 32A-32D, and fed through the separation chamber 34 to the next chamber 32A, 32B, 32C or 32D to perform the similar film forming process. The wafer W thus treated is mounted on the wafer cassette of the load lock chamber 38, and the wafer cassette is taken out to the outside, thereby completing the overall process.
Such a multi-chamber type sputtering device has a restriction that the number of chambers which can be equipped is limited to three or four. Accordingly, when a multilayered film having four layers or five layer or more is formed, it is necessary to continuously form different kinds of metal films in the same chamber.
Particularly when a Ti film and TiN film are continuously formed (hereinafter referred to as "continuous formation of Ti/TiN film"), the Ti/TiN film is formed by the following process because the continuous formation thereof is relatively easy. That is, in this process, a chamber in which a Ti target is mounted is used, and argon gas (hereinafter referred to as "Ar gas") is introduced in a Ti film forming step. Further, reaction gas containing a mixture of Ar gas and nitride gas (hereinafter referred to as "N.sub.2 gas") is introduced in a TiN film forming step, thereby forming a TiN film by a reactive sputtering method.
That is, when the Ti/TiN film is continuously formed, the Ti target is first sputtered while Ar gas flows, thereby forming the Ti film on the wafer, and then mixture gas of Ar gas and N.sub.2 gas flows to sputter the Ti target whose surface is nitrided, thereby continuously forming the TiN film on the Ti film.
The TiN film is roughly classified into a nitride mode TiN film and a metallic mode TiN film from the viewpoint of film quality. The nitride mode TiN film is defined as a TiN film having high barrier performance which is obtained by sputtering Ti target while sufficiently exposing the surface of the Ti target to N.sub.2 plasma to nitride the surface of the Ti target. On the other hand, the metallic mode TiN film is defined as a TiN film obtained by sputtering target containing a large amount of Ti components such as Ti.sub.2 N or the like. The selective formation of the nitride mode TiN and the metallic mode TiN can be performed by adjusting the ratio of Ar gas and N.sub.2 gas or setting the flow rate of N.sub.2 to a predetermined rate or more.
The TiN film which has been hitherto used as a wiring film is the nitride mode TiN film having higher barrier performance. Accordingly, when the Ti/TiN film is continuously formed in one chamber in the above manner, it is a technical great problem whether the TiN film formed has desired film quality or not, that is, whether the TiN film formed is the nitride mode TiN film or the metallic mode TiN film.
Next, the time variation of DC power, N.sub.2 gas flow rate, Ar gas flow rate and the internal pressure in the chamber in a Ti film forming step, a TiN film forming step and a Ti film forming step when a Ti/TiN/Ti film is formed by a conventional three-layer continuous forming method of Ti/TiN/Ti film will be described with reference to FIG. 3.
FIG. 3 is a time chart for the DC power, the N.sub.2 gas flow rate, the Ar gas flow rate and the internal pressure in the chamber in the Ti film forming step, the TiN film forming step and the Ti film forming step.
As shown in FIG. 3, at the shift time from the Ti film forming step to the TiN film forming step and at the shift time from the TiN film forming step to the Ti film forming step, the set values of the Ar gas flow rate and the N.sub.2 gas flow rate are changed to form the respective films under the optimum film forming conditions, respectively.
In the conventional method, however, as shown in the time chart of the internal pressure of the chamber, at the shift time from the Ti film forming step to the TiN film forming step, a temporary variation in pressure occurs in the process chamber when the gas type is changed from Ar gas to N.sub.2 gas, and the TiN film thus formed is not the desired nitride mode TiN film, but the metallic mode TiN film in some cases. In such a situation, the nitride mode TiN having high barrier performance cannot be formed stably, so that Al may be diffused from a wiring layer into a substrate to thereby change the transistor characteristics.